Corynebacterium sp., in particular, Corynebacterium glutamicum, is a Gram-positive microorganism used for the production of L-amino acids. L-amino acids such as L-lysine have been widely used for the production of animal feeds, medicines for humans, pharmaceutical industry, etc, and are mass-produced by a genetic engineering method using a Corynebacterium strain. Increasing demand for L-amino acids due to industrial development has led to the development of improved Corynebacterium strains for more effective and economical production of L-amino acids.
In general, the L-amino acid production of Corynebacterium has been enhanced by introduction of particular DNA, such as L-amino acid biosynthesis-related genes, into a Corynebacterium strain or by improvement of its activity. For example, Korean Patent Publication Nos. 2001-51915 and 2001-62279 disclose methods for enhancing the productivity of L-amino acid from Corynebacterium by the under-expression of sucC and sucD gene and zwa2 gene derived from Corynebacterium glutamicum. Korean Patent Publication No. 2001-62272 discloses a method for enhancing the productivity of L-amino acid from Corynebacterium by the overexpression of zwa1 gene derived from Corynebacterium glutamicum. Japanese Patent No. 1995-121228 discloses a method for introducing a gene encoding citric acid synthase derived from Escherichia coli. 
Meanwhile, Corynebacterium sp. is able to utilize sucrose, glucose, and fructose as carbon sources. Among them, sucrose is phosphorylated by a phosphotransferase system (PTS) and transported into the cell. Subsequently, phosphorylated sucrose is hydrolyzed by invertase to glucose-6-phosphate and fructose. The produced glucose-6-phosphate enters glycolysis, but unphosphorylated fructose is exported from the cell. It is phosphorylated by a PTS, and then transported into the cell, and utilized in glycolysis. Utilization of fructose as a carbon source requires a relatively complex metabolic pathway, because Corynebacterium sp. has no fructokinase activity (Appl Environ Microbiol. (1996) 62:3878-3880). On the other hand, in fructokinase-expressing bacteria, sucrose is hydrolyzed by invertase to glucose-6-phosphate and fructose, and fructose is phosphorylated by fructokinase. Subsequently, glucose-6-phosphate and phosphorylated fructose can enter the glycolytic pathway.
The use of fructose as a carbon source for the cultivation of Corynebacterium sp. has a problem in that it requires unnecessary energy consumption due to the complex metabolic pathway, and thus many studies have been conducted to solve this problem. For example, the present inventors developed a method of producing L-lysine using a transformed strain that is prepared by introduction of a fructokinase gene derived from Clostridium acetobutylicum or Bacillus subtilis into Corynebacterium sp. (Korean Patent No. 564805). However, subsequent studies showed that Corynebacterium sp. transformed with the fructokinase gene has very low fructokinase activity, and upon the use of sucrose as a carbon source for the cultivation of Corynebacterium sp., a portion of the fructose derived from sucrose is converted into fructose-6-phosphate, and the rest is phosphorylated by a PTS outside the cell and subsequently transported into the cell, like in the wild-type, and thus the introduction of the fructokinase gene does not provide a sufficient outcome. Therefore, there is a need to explore other fructokinase genes that show sufficient activity of converting fructose into fructose-6-phosphate in Corynebacterium sp.
The desired fructokinase genes were identified, resulting from the studies on genes mediating sucrose uptake and hydrolysis to impart a sucrose-assimilating ability, and are exemplified by scr regulon found in Salmonella, Klebsiella pneumonia, and Erwinia amylovora (J. Bacteriol., 151:68-76, 1982; Mol. Microbiol., 2:1-8, 1988; J. Bacteriol., 173:7464-7470, 1991; J. Gen. Microbiol., 134:1635-1644, 1988; J. Bacteriol., 182:5351-5358, 2000; U.S. Pat. No. 7,179,623), cscregulon derived from Escherichia sp. (Appl. Environ. Microbiol., 58:2081-2088, 1992; U.S. Pat. No. 6,960,455), and scr regulon and sac operon derived from Gram-positive microorganism, Streptococcus mutans (J. Bacteriol., 171:263-271, 1989). Among them, two fructokinase genes (cscK and mak) were found in Escherichia sp. cscK is a fructokinase gene belonging to csc regulon, and is known to be involved in sucrose metabolism, together with cscB (proton symport-type sucrose permease) and cscA (sucrose hydolase) (J. Bacteriol., 184: 5307-5316, 2002). mak is a gene encoding mannokinase, and the mannokinase is known to have an activity of converting hexose such as mannose, fructose, and glucose into a 6-phospho-ester form (Mol. Microbiol., 5:2913-2922, 1991).